1. Field of the Invention
The present invention relates to switch devices for power tools, such as hand-held power screwdrivers.
2. Description of the Related Art
A known power screwdriver has a tool body having an electric motor disposed therein. A handle protrudes laterally from the tool body. A trigger-type switch lever is mounted to a base portion of the handle. A user can operate the switch lever with his or her fingers to push a switch knob of a switch body assembled within the handle, so that the electric motor is started. Then, a driver bit mounted to a spindle at a position on the side of the front end of the tool body rotates in a driving direction. In order to enable a screw loosening operation in addition to a screw fastening operation, the electric motor can rotate in a reverse direction to rotate the spindle in a screw loosening direction.
An on/off switching circuit and a normal/reverse switching circuit for the motor are disposed within the switch body that is assembled within the handle. Shifting the trigger-type switch lever in forward and rearward directions can operate the switch knob that protrudes laterally from the switch body, so that the on/off switching circuit can be operated. A normal/reverse switching lever can be rotated in forward and rearward directions to operate an electric contact device disposed at the upper portion of the switch body, so that the normal/reverse switching circuit can be operated. In general, the normal/reverse switching lever is rotatably supported on the upper portion of the switch body and assembled with the switch body.
In order to improve the waterproof performance and the dustproof performance of the switch body, various techniques are proposed in Japanese Laid-Open Patent Publications Nos. 4-368727, 9-17280, 9-320398 and 2001-410271.
Although the techniques proposed in the above publications may provide waterproof structures for the switch body, they do not provide sufficient waterproof structures at a position where the normal/reverse switching lever is mounted. Thus, according to the proposed techniques, waterproof or dustproof performance of the switch case are achieved by configuring the switch case to have case halves that are joined to each other by welding or adhesion. Therefore, the on/off switching circuit can be sealingly contained in the switch case. However, the contact device of the normal/reverse switching circuit operable by the normal/reverse switching lever is exposed outside at the upper portion of the switch body, and therefore, waterproofing of the switch device about the normal/reverse switching lever is still required.
Therefore, there is a need in the art for a switch device that has an improved waterproof performance.